A.According to the National Roofing Contractors Association, when the rake edge of a pitched roof intersects a vertical wall, #15 felt should be laid under the shingles, extending 3 to 4 inches up the vertical wall. Metal step flashing (flashing shingles) should be used, with one flashing shingle for each row of shingles. The flashing shingle should be bent to extend under the asphalt shingles on the roof about 2 inches, and 4 inches up the vertical wall. Each metal shingle should be placed slightly up-roof from the bottom edge of the asphalt shingle which overlaps it. Nail the flashing shingle with one nail along the upper end of the vertical leg, as shown in the illustration.

The siding should be brought down over the flashing shingle to serve as a counterflashing, but cut the siding back a couple of inches, far enough to permit painting the ends of the wood siding. This will prevent water from wicking into the ends. If vinyl or metal siding is used, the flashing should be sealed to the sheathing with caulk or butyl tape. Vinyl and metal siding are not waterproof, and water blowing through the joints can run down the sheathing and behind the flashing.